Variation of the FeMn ratio of ferromanganese crusts from the Central North Pacific: implication for paleoclimate changes

Contents of Fe, Mn and other elements in four ferromanganese crusts recovered from the central North Pacific are analyzed at high depth-resolution by electron microprobe for reconstructing factors controlling their deposition. Manganese (IV) in hydrogenetic ferromanganese crusts is mainly supplied as colloidal precipitates from the Oxygen Minimum Zone (OMZ), which concentrates high amounts of dissolved Mn (II). The iron is derived from carbonate dissolution and silicate particles of eolian dust. An increase in paleoproductivity during cooler climate would potentially lead to a decrease in Mn deposition due to enlargement of the OMZ which has a “temporary storage” effect for Mn. On the other hand, not affected by the OMZ, the iron entering the Fe-Mn crust would likely increase with the eolian dust input and surface productivity at glacial stages. As a result, the increasing FeMn ratio should indicate a cooling climate. This is supported by the following observations. In the profile of the past 1 Ma, the variations of FeMn ratio coincide with benthic oxygen isotope fluctuation in glacial-interglacial cycles. Three episodes with high FeMn ratios, approximately at 2.6, 1.8 and 0.8 Ma, are detected within the past 3 Ma and coincide with major climate transitions and cooling events. The secular evolution pattern of FeMn ratio in the Cenozoic is similar to the Pb isotope evolution which is mainly controlled by eolian dust and related to climate. The FeMn evolution pattern is also broadly consistent with the global deep-sea oxygen isotope records. Therefore, FeMn ratio recorded in the ferromanganese crusts may be a new proxy for climate change.     

Late Cenozoic history of deep water circulation in the western North Pacific: Evidence from Nd isotopes of ferromanganese crusts

Despite its importance in regulating the global climate, the past deep ocean circulation in the western North Pacific has still been poorly understood. Nd isotopes of ferromanganese crusts have been proven to be a good proxy to monitor paleoceanic circulation changes. In this study, late Cenozoic Nd isotopic records are recovered from two ferromanganese crusts located near Mariana arc but at different water depths (MKD13: 1530 m, MDD53: 2700 m), and their implications for paleocirculation change in this area are explored. From the early to late Miocene, Nd isotopic compositions of MDD53 remained stable, and they were also characterized by the least radiogenic signatures ( Nd4.0 to5.0) compared to crusts of similar water depths in the Miocene North Pacific. Afterward, an abrupt increase in its Nd value occurred in the Pliocene. In contrast, Nd isotopes of MKD13 became more radio- genic with time in the Miocene and were almost invariable thereafter. The continual increase in Nd of shallower crust MKD13 is interpreted as reflecting progressive closure of Indonesian Seaway in the Miocene, while the deep western boundary current sourced from the Southern Pacific may have dominated Nd isotopes of deeper crust MDD53 during the same time interval. The lack of Nd isotopic variation of MKD13 in the Pliocene indicates that there were no changes in Nd sources in shallower waters and the final restriction between the Indian and Pacific may have only occurred since then. Therefore the observed large shift to more radiogenic Nd isotopes of MDD53 in the Pliocene should not be resulted from changes in vertical input from shallower to deeper water. Instead, a decreased ventilation of deep southern component current along the studied water depth range (~2700 m) may have continued in the Pliocene.     

Os isotopic compositions of a cobalt-rich ferromanganese crust profile in Central Pacific

Cobalt-rich ferromanganese crusts occur throughout the global ocean on seamounts, ridges, and plateaus where currents have kept the rocks swept clean of sediments for millions of years. Crusts are important as a potential re-source for primarily cobalt, but also for titanium, nickel, REE, PGE, and other elements. Most Co-rich crusts pre-cipitate at water depths of about 1000-3000 m, and are easy to be exploited. Besides the high cobalt contents compared to abyssal Fe-Mn nodules, exploitati…     

Petrogenesis of the Neoproterozoic bimodal volcanic rocks along the western margin of the Yangtze Block： New constraints from Hf isotopes and Fe/Mn ratios

High-precision major element and Hf isotope data are reported for the Neoproterozoic Suxiong volcanic rocks along the western margin of the Yangtze Block. These volcanic rocks have variable εHf（T） values and Fe/Mn ratios. The relatively primitive basalts have high Fe/Mn ratios and high Hf-Nd isotopic compositions, indicating that they were generated by partial melting of garnet clinopyroxene in mantle plume at high pressure. Thus, the Suxiong basalts are genetically related to the proposed Neoproterozoic superplume. On the contrary, a few differentiated basalts have low Fe/Mn ratios and low Hf-Nd isotopic compositions. They are likely to experience assimilation-fractional crystallization process. The Suxiong rhyolites have consistent Hf and Nd model ages of 1.3-1.4 Ga. They are likely generated by shallow dehydration melting of pre-existing young arc igneous rocks associated with the basaltic underplating/intrusion in a continental rift.     

Growth ages of ferromanganese crusts from the western and central Pacific： Comparison between nannofossil analysis and ^10Be dating

Based on results of nannofossil analysis and 10Be dating in ferromanganese crusts M1-1 and A1-1 (no nannofossils were found in it),from the western and central Pacific respectively,it is found that the crust growth ages from nannofossil biostrati-graphy agree well with those based on 10Be isotope analysis. Both crusts have three growth layers,and the oldest layer was deposited in Miocene at about 12.80 Ma. The maximum,minimum,and average growth rates of crust A1-1 (from the central Pacific) are 8.11,1.92 and 3.47 mm/Ma,and those of crust M1-1 (from the western Pacific) are 2.93,0.47,and 0.94 mm/Ma.     

海底构造运动的指示物--多金属结核中的CaCO3/Fe2O3和MgCO3/Fe2O3比值

研究了中太平洋3个多金属结核中共5个侧面CaCO3/Fe2O3和MgCO3/Fe2O3比值的深度分布。根据CaCO3的热力学性质，我们认为结核中的CaCO3/Fe2O3比值与沉积物中的CaCO3保存量类似，与古水深之间存在着负相关关系。结核中由表及里，CaCO3/Fe2O3比值逐渐增大，说明结核所处海域，即中太平洋海盆的水深逐渐增大，这在一定程度上也反映了中太平洋海盆的下降，因而结核中的CaCO3/Fe2O3比值也许可以作为海底构造运动的指示物。而MgCO3/Fe2O3比值与其有着良好的一生，说明其与CaCO3/Fe2O3比值一样，也可以作为海底构造运动的指示物。     

The interdecadal trend and shift of dry/wet over the central part of North China and their relationship to the Pacific Decadal Oscillation （PDO）

Based on monthly precipitation and monthly mean surface air temperature (SAT),the dry/wet trends and shift of the central part of North China and their relationship to the Pacific Decadal Oscillation (PDO) from 1951 to 2005 have been analyzed through calculating surface wetness index (SWI). The results indicate that there was a prominent drying trend and an abrupt change in the analysis period. A per-sistent warming period with less precipitation from the mid and late 1970s to present was found,and a shift process exists from the wet to the dry in the central part of North China during 1951-2005. The transition is located in the mid to late 1970s,which should be related to the shift variation of large-scale climate background. The correlation analysis has brought about a finding of significant correlativity between PDO index (PDOI) and SAT,precipitation and SWI in this region. The correlation exhibits that the positive phase of PDOI (warm PDO phase) matches warming,less precipitation and the drought period,and the negative PDOI phase corresponds to low SAT,more precipitation and the wet period. The duration of various phases is more than 25 years. The decadal variation of sea surface temperature (SST) in the North Pacific Ocean is one of the possible causes in forming the decadal dry/wet trend and shift of the central part of North China.     

The Effect of Oxidation／Reduction Disposing on Optical Properties of Mg： Fe： Mn： LiNbO3 Crystals

The congruent tri-doped Mg: Mn: Fe: LiNbO3 crystal has been grown by Czochralski method. Some crystal samples are reduced in Li2CO3 powder at 500℃ for 24 hours or oxidized for 10 hours at 1100 ℃ in Nb2O5 powder. Compared with As-grown Mg:Mn:Fe:LiNbO3, the absorption edge in UV-Vis. absorption spectrum of the oxidized sample and the reduced shifts to the violet and the red, respectively. Reduction increases the absorption of crystals in visible light region. In two-wave coupling experiments, the writing time, maximum diffraction efficiency and the erasure time of crystal samples in the same conditions are determined. The results indicate that oxidation and reduction disposing has great effect on the holographic recording properties of these crystals. The reduced crystal exhibits the fastest response time of 160 s anmng the crystal series. The mechanism of post-disposing effect on the holographic recording properties of Mg:Mn:Fe:LiNbO3 crystals are investigated.     

地表典型铁锰沉积物岩石漆的研究历程与展望

岩石漆是地表风化环境中最具代表性的铁锰质沉积物,一直以来在学界广受关注.近几十年来,随着表征技术的不断发展,岩石漆的研究也取得了显著成果.简述了岩石漆的研究历程,着重介绍了岩石漆的形貌特征、地球化学特征、矿物组成和成因机制.产于地表暴露环境中的岩石漆是地表关键带的重要组成部分,是各种物质发生交互作用的关键性场所.因此,...     

The Dongcaohe ophiolite from the North Qilian Mountains： A fossil oceanic crust of the Paleo-Qilian ocean

The Dongcaohe ophiolite, located at the south of the North Qilian subduction complexes, is a tectonic block with an exposed area of about 3 km×6 km. It consists of an intrusive section overlain by an ex- trusive section. The lower part of the intrusive section consists of cyclic layers of cumulate dunites, troctolites, anorthosites, anorthositic gabbros, and gabbros with small discordant dunite and troctolite bodies. This layered sequence grades upward to isotropic gabbros and gabbronorites, which are overlain by the extrusive sequence of diabasic sheeted dikes and basaltic lavas. The overall mineral crystallization sequence was olivine±Cr-spinel, plagioclase, clinopyroxene, orthopyroxene, and Fe-Ti oxides. The Cr-spinel (Mg#: 42-66, Cr#: 41-57) in these layered cumulates and present-day abyssal peridotites have similar compositions. Also, the compositional variations of the plagioclase and cli- nopyroxene in the intrusive section reflect crystallization from melts compositionally similar to the present-day ocean basalts. Moreover, the rare earth element (REE) and multi-element distribution pat- terns of the intrusive and extrusive lithologies in the Dongcaohe ophiolite are consistent with crystal- lization of mid-ocean ridge basalts. The zircon grains separated from the gabbronorite have an SHRIMP average 206Pb/238U weighted age of 497 ± 7 Ma, which is considered as the tectonic emplacement age of the Dongcaohe ophiolite. The field occurrence, mineral and whole-rock compositions indicate that the Dongcaohe ophiolite represents a well-persevered oceanic crustal fragment composed of a complete oceanic crustal section of layered cumulates at bottom upgrading through isotropic cumulates to sheeted dikes and lava flows.     

低应变速率下锰硫比对低碳钢高温塑性的影响

研究了在低应速率下锰硫比对低碳钢高温塑性的影响,实验结果表明,不同测试温度下锰硫比对钢的高温塑性的影响不同。按其影响规律,可分为４个温度区域即：（１）１３５０－１４００℃,锰硫比越高,塑性越差;（２）１０００－１３５０℃,锰硫比对塑性无影响;（３）８００－１０００℃,锰硫比越高,塑性越好;（４）６００－８００℃,锰硫比越高,塑性越差,同时还对锰硫比对高温塑性的影响机理进行了分析。     

Hf isotopes of the 3.8 Ga zircons in eastern Hebei Province, China： Implications for early crustal evolution of the North China Craton

Zircon U-Pb dating indicates that the fuchsite quartzite in eastern Hebei Province was derived from weathering and erosion of the 3.6-3.8 Ga granitic rocks. In-situ zircon Hf analyses show that the Lu-Hf isotopic system remained closed during later thermal disturbances. Zircons with concordant ages have Hf isotopic model ages of about 3.8 Ga, suggesting a recycling of this ancient crust. The -3.8 Ga zircons have similar Hf isotopic compositions to those of chondrite, indicating that their source rocks （granitic rocks） were derived from partial melting of the juvenile crust which originated from a mantle without significant crust-mantle differentiation. Therefore, it is proposed that there was no large-scale crustal growth before -3.8 Ga in eastern Hebei Province. Considering zircon Hf isotopic data from other areas, it is concluded that the most ancient crust in the North China Craton probably formed at about 4.0 Ga, and the possibility to find crust older than 4.0 Ga is very limited.     

Dust storm in Asia continent and its bio-environmental effects in the North Pacific： A case study of the strongest dust event in April, 2001 in central Asia

The iron hypothesis, first proposed by John Martin in 1990[1], suggests that some surface oceans such as North and Equatorial Pacific Oceans have high nutrient but low chlorophyll (HNLC). Thus iron coming from terrestrial dusts is the primary factor limit…     

中原地区距今5000-4000年间古环境重建的软体动物化石证据

河南孟津邙山黄土台塬上发现的全新世湖沼沉积保存有丰富的古环境信息。根据其中所含水生、两栖与陆生软体动物化石的系统研究,作者着重讨论了距今5000-4000年间古代湖沼演化的历史,并进一步根据软体动物化石的古生态分析,指出古代湖沼的演化与当时气候的变化一致。这一研究为探讨中原地区环境演变的历史及华夏文明起源的环境背景提供了重要的资料。     

冀北赤城红旗营子群黑云斜长片麻岩的黑云母~(40)Ar/~(39)Ar年龄及其地质意义

探讨冀北赤城红旗营子群是否经历了印支期的构造热事件。通过对冀北赤城红旗营子群黑云斜长片麻岩样品进行的黑云母40 Ar/39 Ar年龄测定,获得其坪年龄和等时线年龄分别为(238.63±1.44)Ma和(238.77±1.71)Ma,两者基本一致。此年龄数据是黑云斜长片麻岩在晚古生代角闪岩相区域变质作用之后所经历印支期构造热事件的记录。综合分析冀北岩浆作用及其地质年代学特征,认为它可能与区域上同时期的酸性岩浆活动有关,是后者为此次构造热事件提供了必要的热源。     

纳米Fe/Ni双金属的制备及其对水中2,4-二氯酚的还原效果

 采用液相还原法制备了纳米Fe/Ni双金属材料,分析了FeCl₂浓度、n（Ni）/n（Fe）和n（NaBH₄）/n（FeCl₂）物质的量之比对制得的Fe/Ni双金属还原水中2,4-二氯酚（2,4-DCP）效果的影响,明确了Fe/Ni对2,4-DCP的还原脱氯途径。结果表明：在FeCl₂浓度为3 mol/L、n（Ni）/n（Fe）=4%,n（NaBH₄）/n（FeCl₂）=1的条件下制备的Fe/Ni双金属对2,4-DCP的去除率接近100%,且其中95%被还原成苯酚。纳米Fe/Ni为球形颗粒,粒径约为50 nm,在自身磁力作用下相互链接为枝状,又通过静电稳定作用分散聚集,形成海绵状多孔结构,BET比表面积为44.8 m²/g。纳米Fe/Ni还原2,4-DCP的途径主要是苯环上的2个C-Cl键依次被加氢还原,先脱去一个氯生成2-氯酚或4-氯酚,再进一步脱氯转化为稳态的苯酚。     

凹凸棒土负载纳米Fe/Ni的制备及其去除水中Zn(Ⅱ)性能研究

采用液相还原法制备以凹凸棒土为载体的纳米双金属Fe/Ni复合材料,通过Zn(Ⅱ)静态吸附试验,确定了除Zn(Ⅱ)效果最佳的Fe/Ni@ATP复合材料,即纳米铁与凹凸棒土的负载比为1∶2、Fe/Ni双金属中Ni掺杂比为2%,并考察了Zn(Ⅱ)初始浓度、pH及环境温度对该复合材料去除水中Zn(Ⅱ)效果的影响。结果表明,经过凹凸棒土负载和掺杂Ni改性以后,Fe/Ni@ATP复合材料的Zn(Ⅱ)去除率显著提高,颗粒团聚状况得到改善,比表面积明显增加。在实验条件范围内,较高的溶液pH值、环境温度以及较低的Zn(Ⅱ)初始浓度均有利于Fe/Ni@ATP复合材料对Zn(Ⅱ)的去除。该过程符合Langmuir吸附等温模型,吸附机理为零价铁表面氧化物与Zn(Ⅱ)的配合作用,此外,水中Zn(Ⅱ)也可以通过生成Zn(OH)_2沉淀的形式去除。     

Vertical adaptive radiation in ocean Prochlorococcus: Evolutionary implications of the Chl b/a ratio from molecular evidence

Prochlorococcus is a marine cyanobacterium of global significance. Two ecotypes are adapted to either high-light (HL) or low-light (LL) conditions. The ratio between chlorophyll (Chl) a and b is a distinguishing characteristic of these two ecotypes. However, how this ratio evolved in Prochlorococcus during this ecotype differentiation remains unclear. Our analyses reveal that the ancestor of Prochlorococcus was typically low-light adapted. The LL ecotype showed a stagnant evolution, and the HL ecotype was recently diverged. There was an adaptive radiation after directional evolution in the Chl b/a ratio regulation. Recombination in chlorophyllide a oxygenase (CAO) and positive selection on Clp protease contributed to the directional evolution of Prochlorococcus. The recombinant fragments of CAO were correlated with a large group of shared coevolving sites. Evidence of positive selection was found in both subunits of Clp. Chl b/a ratio evolution, as annotated by molecular evidence, appears to be among the crucial reasons that explain how Prochlorococcus has become the dominant photosynthetic organism in the ocean.     

A chemical index of weathering without effect of wind sorting: Fe/Mg ratios in the acid-insoluble phases of loess deposits

Chemical analysis of acid-insoluble fractions in loess and paleosols shows that concentrations of Fe and Mg were under control of wind sorting and post-depositional weathering-pedogenesis. The former caused Fe and Mg concentrated in the finer grain-size fractions, displaying synchronous variations, while the latter made Fe and Mg separated, leading to Fe retained in the weathered section and Mg leached out. Therefore, Fe/Mg ratios in the acid insoluble fraction of loess and paleosols can eliminate the effect of wind sorting and serve as an excellent proxy record on intensity of weathering-pedogenesis. Based on calculation, leaching percentage of Mg in the paleosol S1 from the Luochuan, Xifeng and Huanxian sections is 15%, 11% and 2%, respectively, and on average 9% for the paleosols S₂—S₁₄ from the Luochuan section, with the highest value amounting to 22% in S_5-1, suggesting the strongest weathering-pedogenesis.     

Fe对Co／HZSM—5在甲烷选择还原NO中活性的影响

用浸渍法制备了Fe-Co/HZSM-5催化剂，考察了有氧条件下，在甲烷选择还原NOx的反应中，Fe的加入对Co/HZSM-5活性的影响，发现在较低温度下，Fe与Co/HZSM-5之间存在着协同效应。